Description of problem:
ran a replay tool to find another btrfs-issue, when this turned up.

Additional info:
reporter:       libreport-2.1.4
kernel BUG at fs/btrfs/extent_io.c:4138!
invalid opcode: 0000 [#1] SMP 
Modules linked in: nls_utf8 isofs vfat fat fuse usb_storage nf_conntrack_netbios_ns nf_conntrack_broadcast ipt_MASQUERADE ip6table_nat nf_nat_ipv6 ip6table_mangle ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 iptable_nat nf_nat_ipv4 nf_nat iptable_mangle nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ebtable_filter ebtables ip6table_filter ip6_tables rfcomm bnep snd_hda_codec_hdmi snd_hda_codec_idt iTCO_wdt iTCO_vendor_support mmc_block dell_wmi sparse_keymap ppdev dell_laptop dcdbas mperf coretemp kvm_intel arc4 iwldvm kvm mac80211 microcode snd_hda_intel snd_hda_codec uvcvideo cdc_mbim snd_hwdep snd_seq videobuf2_vmalloc videobuf2_memops i2c_i801 videobuf2_core videodev media btusb cdc_ncm snd_seq_device usbnet bluetooth mii snd_pcm iwlwifi cdc_wdm cdc_acm sdhci_pci cfg80211 sdhci lpc_ich mfd_core mmc_core snd_page_alloc rfkill e1000e snd_timer snd ptp mei soundcore pps_core wmi parport_pc parport uinput binfmt_misc btrfs libcrc32c xor zlib_deflate raid6_pq dm_crypt crc32_pclmul i915 crc32c_intel ghash_clmulni_intel i2c_algo_bit drm_kms_helper drm i2c_core video
CPU 2 
Pid: 10799, comm: btrfs-endio-wri Not tainted 3.9.4-300.fc19.x86_64 #1 Dell Inc. Latitude E6320/050F4T
RIP: 0010:[<ffffffffa019e401>]  [<ffffffffa019e401>] btrfs_release_extent_buffer_page.constprop.54+0x101/0x110 [btrfs]
RSP: 0018:ffff88011f66dc48  EFLAGS: 00010202
RAX: 0000000000000001 RBX: ffff8801dcdb6d20 RCX: 0000000000000003
RDX: 0000000000000000 RSI: 0000000000059a91 RDI: ffff8801dcdb6d20
RBP: ffff88011f66dc68 R08: 0000000000001000 R09: ffff88014e3a48d8
R10: 0000000000000000 R11: 0000000000000000 R12: ffff880211d57958
R13: ffff8801dcdb6d20 R14: 0000000000000005 R15: ffff8801f96ebbd0
FS:  0000000000000000(0000) GS:ffff88022dc40000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f580a39c000 CR3: 0000000001c0c000 CR4: 00000000000407e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process btrfs-endio-wri (pid: 10799, threadinfo ffff88011f66c000, task ffff88006ca28000)
Stack:
 ffff8801dcdb6d20 ffff880211d57958 ffff8801f96ebbd0 ffff880217d97800
 ffff88011f66dc88 ffffffffa019e446 ffff8801dcdb6d20 ffff8801f96ebbd0
 ffff88011f66dca0 ffffffffa01a3bef 0000000000000000 ffff88011f66dcc8
Call Trace:
 [<ffffffffa019e446>] release_extent_buffer.isra.33+0x36/0xb0 [btrfs]
 [<ffffffffa01a3bef>] free_extent_buffer+0x4f/0xa0 [btrfs]
 [<ffffffffa015edd5>] btrfs_release_path+0x25/0xb0 [btrfs]
 [<ffffffffa018832b>] insert_reserved_file_extent.constprop.56+0x20b/0x290 [btrfs]
 [<ffffffffa0191b8e>] btrfs_finish_ordered_io+0x50e/0x990 [btrfs]
 [<ffffffff8106d102>] ? del_timer_sync+0x52/0x60
 [<ffffffff816429d9>] ? schedule_timeout+0x179/0x2c0
 [<ffffffff81132209>] ? mempool_free+0x49/0x90
 [<ffffffffa01921f5>] finish_ordered_fn+0x15/0x20 [btrfs]
 [<ffffffffa01b110b>] worker_loop+0x12b/0x510 [btrfs]
 [<ffffffffa01b0fe0>] ? btrfs_queue_worker+0x300/0x300 [btrfs]
 [<ffffffff81080370>] kthread+0xc0/0xd0
 [<ffffffff810802b0>] ? insert_kthread_work+0x40/0x40
 [<ffffffff8164e32c>] ret_from_fork+0x7c/0xb0
 [<ffffffff810802b0>] ? insert_kthread_work+0x40/0x40
Code: 20 75 2a f0 41 80 64 24 01 f7 49 c7 44 24 30 00 00 00 00 4c 89 e7 e8 af e6 f9 e0 eb be 0f 1f 44 00 00 5b 41 5c 41 5d 41 5e 5d c3 <0f> 0b 0f 0b 0f 0b 0f 0b 0f 1f 80 00 00 00 00 66 66 66 66 90 55 
RIP  [<ffffffffa019e401>] btrfs_release_extent_buffer_page.constprop.54+0x101/0x110 [btrfs]
 RSP <ffff88011f66dc48>